Geology Exam 2: Rivers

Slope and river zones

Headwaters, transfer zone, and depositional zone.

Channel incisions

Can be deep, even if water in the channel is not deep.

Catchment

The drainage area that feeds into a single river.

River mouth

Where a river empties into another body of water.

Delta

Area at a river mouth where the river splits to distribute water and sediment.

Confluence

The location where two rivers or streams come together.

River discharge

The amount of water flowing through a river.

Peak rainfall vs. peak discharge

Peak rainfall occurs first; peak discharge occurs later as runoff collects.

Catchment area

The total land area where precipitation drains into a river or stream.

Catchment-scale discharge equation

Q = P × A × C (P=precipitation, A=catchment area, C=runoff coefficient).

Rainfall amount vs. discharge anomaly

Lighter rainfall over a larger catchment can produce more discharge than heavy rain.

Runoff coefficient (C)

A value representing how readily precipitation runs off land into a river.

Pavement effect on runoff

Increases runoff coefficient because water cannot infiltrate the ground.

Vegetation effect on runoff

Lowers runoff coefficient by allowing more water to infiltrate the soil.

Urbanization and flooding

Paved surfaces speed up runoff, leading to quicker water arrival and higher peak discharge.

Green infrastructure and flooding

Trees and vegetation increase infiltration and slow runoff before it reaches rivers.

Aquatic vegetation impact

Increases friction, decreases flow velocity, reduces erosion, and encourages sediment deposition.

Riparian vegetation impact

Deep roots hold riverbank sediment together and reduce bank erosion.

Aquatic vs. riparian vegetation

Aquatic vegetation slows water/promotes deposition; riparian vegetation stabilizes banks.

Flow velocity and sediment size

Faster water transports coarser sediment; slower water transports finer sediment.

Particle size and settling rate

Larger particles settle faster; smaller particles settle more slowly.

Mud erosion

Clay particles are cohesive, so high flow velocity may be required to initially erode mud.

Mud transport

Once suspended in water, mud remains suspended even at relatively low velocities.

Dissolved load

Material chemically dissolved in river water, such as tannins.

Suspended load

Fine sediment, like silt and clay, carried within the water column.

Bedload

Coarser sediment that moves along the riverbed by rolling, sliding, or bouncing.

Saltation

The bouncing or hopping movement of sediment along a riverbed.

River morphology controllers

Discharge, flow velocity, sediment size/load, slope, vegetation, and bank stability.

River morphology

The shape and physical form of a river channel.

Braided river

Multi-channel river with coarse sediment, high bedload, poor sorting, and unstable channels.

Braided river instability

High/variable flow and large sediment supply cause frequent shifts and erosion.

Meandering river

Usually single-channel, winding river with finer sediment, suspended load, and stable banks.

Anastomosing river

Low-energy, multi-channel river with fine sediment and highly stable, vegetated channels.

Braided vs. anastomosing rivers

Both have multiple channels, but braided are unstable/coarse; anastomosing are stable/fine.

Coarsest sediment rivers

Braided rivers tend to have the coarsest sediment.

Finest sediment rivers

Anastomosing rivers tend to have the finest sediment.

Vegetation and morphology

Vegetation stabilizes banks and channels, favoring meandering or anastomosing patterns.

Water table

The level below which the ground is saturated with groundwater.

River flow and groundwater

Rivers can interact with and receive water from the groundwater table.

Ephemeral river

A river that flows mainly during or immediately after storms, lying above the water table.

Intermittent river

A river that flows seasonally when precipitation raises the water table.

Perennial river

A river that flows year-round because it remains connected to groundwater.

Ephemeral vs. intermittent vs. perennial

Ephemeral = storm flow; intermittent = seasonal; perennial = year-round.

Channel discharge equation

Q = A × V (A = cross-sectional area, V = flow velocity).

Catchment vs. channel discharge

Catchment discharge uses precipitation and drainage area; channel discharge uses area × velocity.

Meander initiation

Small disturbances like logs or boulders can redirect flow and create velocity differences.

Fastest water in a meander

Located along the outside of the bend.

Slowest water in a meander

Located along the inside of the bend.

Cut bank vs. point bar

Cut bank = outside, fast water, erosion; Point bar = inside, slow water, deposition.

Thalweg

The path connecting the deepest parts of a river channel, generally associated with fastest flow.